A typical parallel optical communications module includes a circuit board, such as a printed circuit board (PCB), a leadframe mounted on and electrically coupled to the circuit board, one or more integrated circuits (ICs) mounted on the leadframe, an array of optoelectronic devices mounted on the leadframe, a plurality of bond wires interconnecting the ICs with the circuit board and with the array of optoelectronic devices, and an optics system for coupling light between the ends of a plurality of optical fibers and respective optoelectronic devices of the array.
The optoelectronic devices may be light sources, such as laser diodes or light emitting diodes (LEDs), and/or light detectors, such as photodiodes. The ICs may include a laser diode driver IC and/or a receiver IC. If the parallel optical communications module is a parallel optical transmitter module, the optoelectronic devices are typically either laser diodes or LEDs and the IC is a driver IC that delivers electrical signals to the laser diodes or LEDs to cause them to produce optical data signals. If the parallel optical communications module is a parallel optical receiver module, the optoelectronic devices are typically photodiodes and the IC is a receiver IC that processes the electrical signals produced by the photodiodes to recover the data contained in the optical data signals. If the parallel optical communications module is a parallel optical transceiver module, the optoelectronic devices typically include laser diodes or LEDs and photodiodes, and the ICs typically include a laser diode driver IC and a receiver IC.
When a parallel optical communications module of the type described above is assembled, the optics system must be precisely aligned with the array of optoelectronic devices in order to ensure that the optical data signals are properly coupled between the ends of the optical fibers and the optoelectronic devices. Otherwise, the integrity of the optical data signals will degrade, which will detrimentally affect the performance of the module. Therefore, great care is taken during the assembly process to ensure that the optics system and the array of optoelectronic devices are in precise alignment.
In parallel optical communications modules of the type described above, active alignment systems are typically used to align the optics system with the array of optoelectronic devices during the assembly process. To accomplish the alignment process, a machine vision system of the active alignment system locates fiducial marks on the circuit board and uses them to align the optics system with the circuit board as the optics system is mounted. The fiducial marks are also used by the machine vision system to align the array of optoelectronic devices with the circuit board when the array is mounted on the leadframe. Using the fiducial marks in this manner to precisely position both the optics system and the array of optoelectronic devices on the circuit board should ensure that the optics system and the array of optoelectronic devices are in precise alignment with each other after they have been mounted.
While active alignment systems generally work well for their intended purposes, they are relatively expensive systems that increase the overall assembly cost. Passive alignment processes have also been used to align the optics systems with the optoelectronic device array during the assembly process. Typical passive alignment processes utilize pins on the module or circuit board and openings in the optics system that have reciprocal shapes for receiving the pins. One of the disadvantages of such passive alignment systems is that there are manufacturing tolerances associated with forming the pins and openings. These tolerances tend to accumulate and can result in the shapes and/or positions of the pins and/or the openings not being sufficiently precise to ensure precise alignment between the optics system and the array of optoelectronic devices.
A need exists for a passive alignment method and apparatus that ensure precise alignment between the optics system and the array of optoelectronic devices.